1.Field of the Invention
The present invention relates to a method for the treatment of silane-containing gas for removing or reducing the amount of silanes in the gas.
2. Prior Art
A variety of methods have hitherto been employed for treating gases containing silanes and other harmful substances. These methods include gas absorption, gas adsorption, catalytic oxidation, and incineration.
Gas absorption is a process in which harmful substances are absorbed and decomposed in a scrubber. When the harmful substances are silanes, the absorbing liquid used is often an alkali solution or water. However, problems associated with this approach include the corrosion of equipment by the absorbing liquid and the need to post-treat the sticky material that forms as a result of silane hydrolysis. Hence, equipment maintenance and management costs are incurred.
Gas adsorption, as described in JP-A 291625/1988, is a method for removing harmful substances from a gas by passing the gas through a column packed with adsorbent. However, because sticky material is adsorbed onto the adsorbent, post-treatment and equipment maintenance costs are unavoidable here too.
U.S. Pat. No. 4,515,762 describes a catalytic oxidation process in which combustible substances within a gas are rendered harmless by bringing them into catalytic contact with air to effect oxidative combustion and degradation. However, when this process is used to treat a silane-containing gas, the catalyst becomes poisoned.
U.S. Pat. No. 4,519,999 describes a combustion process in which harmful substances are removed from a waste gas by oxidatively decomposing them under combustion conditions in order to transform them into solid substances such as uncombined elements and oxides. However, if a silane-containing gas is treated by this process, silicic acid is formed in a very fine form that is difficult to separate from the combustion gases. Moreover, when chlorosilanes are present in the gas being treated, hydrogen chloride and chlorine gas form within the combustion gases. Then the combustion step must be followed by further treatment on the residual gas.
Yet another approach is described in U.S. Pat. No. 4,923,687 as a method for removing silane compounds from silane-containing exhaust gases. A silane-containing exhaust gas is reacted with an alcohol in the presence of a metal alcoholate to form tetraalkoxysilanes, which are removed.
All of the above techniques are gas treatment methods for removing or reducing the amount of substances present in a gas. The purpose of these treatment methods is solely to remove or reduce the amount of substances within a gas; none of these methods attempts to recover and reuse silanes from a gas.
JP-B 48568/1988 corresponding to EP 216292 describes a method for treating a gas containing chlorosilanes and hydrogen chloride by subjecting the gas to hydrolysis in aqueous hydrochloric acid as pretreatment, suspending the chlorosilanes, removing the suspended solids, and thereafter, recovering the hydrogen chloride. This method is not intended for the recovery of silanes.